Prior attempts have been made to develop aquaculture systems for growing and harvesting fish by mooring or tethering cage structures to shore piers or anchoring them to the sea floor. For example, U.S. Pat. No. 6,044,798 to Foster et al., issued April 2000, disclosed a floating aquaculture apparatus which is moored by anchors and is submerged in a natural body of water, and U.S. Pat. No. 6,520,115 to Boyd, issued February 2003, disclosed an “Artificial Island Reef Platform” for raising large quantities of pelagic fish with design features that include a large subsurface framework, cabling network, multiple cages and stable anchoring system. Other floating and/or submerged sea cages for aquaculture use are proposed in U.S. Pat. No. 6,044,798 to Foster et al.
An example of a currently used type of near-shore-deployed sea cage is the SEA STATION™ cages made by Ocean Spar, LLC, of Bainbridge Island, Wash. This type of cage typically has a central stem with an air chamber for controlling buoyancy for surfacing or submerging. The bottom of the central stem is tethered to an anchor (or anchors) or grid mooring system on the sea floor. The outer periphery of the cage has mesh netting forming the outer boundaries for the cage. Even when deployed in ocean waters, wastes from the growing fish can become concentrated in the cage volume and the mesh netting may become contaminated and not able to be cleaned efficiently at sea. Prior techniques to clean the top half of ocean fish-growing cages include the technique of releasing the central stem from its anchor tether partially and pumping air into the air chamber in the central stem for buoyancy to propel it upwards toward the ocean surface so that the upper portions of the netting can be exposed for air-drying. While air-drying of the netting does appear to kill parasites that adhere to the netting, cleaning the lower portions of the netting for the cage requires extensive use of divers and specialized high-pressure-washing equipment, which is very costly and time-consuming.
Ocean thermal energy conversion (OTEC) has been used to generate electric power for various ocean and shore industrial uses. An early example of an oceanic heat pump is provided in U.S. Pat. No. 2,006,985 to Claude et al., issued in July 1935. U.S. Pat. No. 4,726,191 to Kawamura, issued in February 1988, disclosed a land-based plant using heat exchange with cold deep well water inducted through ground pipes to generate electricity, and also mentioned that the cold water effluent may also be used for an aquaculture preserve. OTEC systems use a heat pump cycle commonly referred to as the “Stirling” cycle, after the Stirling-cycle engine invented by Robert Stirling in 1817. Various other proposals have been developed for using OTEC-generated power, such as for desalinization plants as described in U.S. Pat. No. 4,302,297 to Humiston, and electricity generation in U.S. Pat. No. 4,441,321 to Ridgway and U.S. Pat. No. 6,202,417 to Beck.